Anatomy & Phys: Ch. 11.4-11.6 - The Nervous System

a. The resting state of a neuron

All voltage-gated Na+ and K+ channels are closed during which of the following stages? a. The resting state of a neuron b. The absolute refractory period c. The repolarization phase of an action potential d. The depolarization phase of an action potential e. The hyperpolarizing phase of an action potential

d. The hyperpolarization phase of an action potential

Excessive potassium efflux as a result of relatively slower closure of the potassium gates corresponds to what part of an action potential curve? a. The depolarization phase of an action potential b. The absolute refractory period c. The repolarization phase of an action potential d. The hyperpolarization phase of an action potential

a. Stronger stimuli generate action potentials more frequently than weaker stimuli.

How can the central nervous system determine whether a particular stimulus is intense or weak? a. Stronger stimuli generate action potentials more frequently than weaker stimuli. b. Action potentials that are created by stronger stimuli travel faster than those created by weaker stimuli. c. Stronger stimuli produce action potentials with greater amplitude than weaker stimuli. d. The central nervous system requires inputs from other sources because it can not detect differences in stimulus strength.

c. Potassium

The movement of which ion through leakage (nongated) channels plays the most important role in generating the resting membrane potential? a. Sodium b. Chloride c. Potassium d. Calcium

b. Group C fibers

Which fiber type consists of small diameter, unmyelinated axons, that propagate nerve impulses slowly? a. Group D fibers b. Group C fibers c. Group A fibers d. Group B fibers

c. the neuron is in the refractory period

A neuron will not respond to a second stimulus of equal strength to the first stimulus to which it has already responded because __________. a. the neuron is myelinated b. action potential generation is an all-or-none phenomenon c. the neuron is in the refractory period d. neurons are self-propagating cells

c. subthreshold stimulus

A stimulus that fails to generate an action potential is called a ________. a. threshold stimulus b. temporal stimulus c. subthreshold stimulus d. spatial stimulus

d. Repolarizing phase

During which phase of an action potential are voltage-gated K+ channels open, while voltage-gated Na+ channels are closed? a. Regeneration b. Depolarizing phase c. Resting state d. Repolarizing phase

a. an autoimmune disease that leads to destruction of the myelin sheaths in the CNS

Multiple sclerosis is __________. a. an autoimmune disease that leads to destruction of the myelin sheaths in the CNS b. a conduction process in myelinated axons where the electrical signal appears to jump from gap to gap along the axon c. an action potential occurring only if enough Na+ enters the cell and threshold is achieved d. rapid automatic responses to a stimulus in which the particular stimulus always produces the same motor response

b. Depolarization phase of an action potential

Na+ channels open during which of the following events? a. The relative refractory period b. Depolarization phase of an action potential c. The repolarization phase of an action potential d. The hyperpolarizing phase of the action potential e. The resting state of a neuron

b. all gated Na+ and K+ channels are closed

The point marked 1, on the figure, can be described as ________. a. K+ rushes out of the cell b. all gated Na+ and K+ channels are closed c. some K+ channels remain open and Na+ channels reset d. Na+ channels are inactivating and K+ channels are open e. Na+ channels are open

c. pump three sodium ions out of the cell for every two ions of potassium it brings into the cell

The sodium-potassium ion pump will __________. a. pump three potassium ions out of the cell for every two sodium ions it brings into the cell b. pump one sodium ion out of the cell for every ion of potassium it brings into the cell c. pump three sodium ions out of the cell for every two ions of potassium it brings into the cell d. pump one potassium ion out of the cell for every ion of sodium it brings into the cell

d. Stronger stimuli generate action potentials more frequently than weaker stimuli. Stronger stimuli generate action potentials more frequently than weaker stimuli. Strong stimuli generate nerve impulses more often in a given time interval than do weak stimuli. Stimulus intensity is coded for by the number of impulses per second—that is, by the frequency of action potentials—rather than by increases in the strength (amplitude) of the individual APs.

How can the central nervous system determine whether a particular stimulus is intense or weak? a. Stronger stimuli produce action potentials with greater amplitude than weaker stimuli. b. The central nervous system requires inputs from other sources because it can not detect differences in stimulus strength. c. Action potentials that are created by stronger stimuli travel faster than those created by weaker stimuli. d. Stronger stimuli generate action potentials more frequently than weaker stimuli.

b. A decrease in the electrochemical gradient would reduce K+ leak so cells would be less negative (more depolarized). A decrease in the electrochemical gradient would reduce K+ leak so cells would be less negative (more depolarized). Potassium ions normally diffuse out of the cell along their concentration gradient from higher intracellular concentration to lower extracellular concentration. K+ flowing out of the cell causes the cell to become more negative inside. If extracellular K+ is increased, the concentration gradient across the membrane is decreased and therefore K+ is less likely to leave the cell. The retention of positively charged ions within the cell would depolarize the membrane.

How would an increased extracellular K+ concentration affect K+ diffusion at leakage (nongated) channels and the membrane potential? a. An increase in the electrochemical gradient would increase K+ leak so cells would be more negative (more hyperpolarized). b. A decrease in the electrochemical gradient would reduce K+ leak so cells would be less negative (more depolarized). c. An decrease in the electrochemical gradient would decrease K+ leak so cells would be more negative (more hyperpolarized). d. An increase in the electrochemical gradient would increase K+ leak so cells would be more negative (more depolarized).

c. a conduction process in myelinated axons where the electrical signal appears to jump from gap to gap along the axon

Saltatory conduction refers to _______. a. impulse propagation following an autoimmune disease that destroys the myelin sheaths in the CNS b. an action potential that occurs only if enough Na+ enters the cell and threshold is achieved c. a conduction process in myelinated axons where the electrical signal appears to jump from gap to gap along the axon d. rapid automatic responses to a stimulus in which the particular stimulus always produces the same motor response e. indirect synaptic responses that are complex, prolonged, and often diffuse as a result of the production of intracellular second-messenger molecules

a. depolarizing graded potential as ions move through nonvoltage-gated channels The point marked 2, on the figure, represents a depolarizing graded potential as ions move through nonvoltage-gated channels. In a depolarizing graded potential, the inside of the cell becomes less negative, as it approaches the threshold value for triggering an action potential. Only the action potential involves voltage-gated channels.

The point marked 2, on the figure, can be described as ________. a. depolarizing graded potential as ions move through nonvoltage-gated channels b. depolarization caused by Na+ flowing through voltage-gated channels into the cell c. hyperpolarizing graded potential as ions move through nonvoltage-gated channels d. repolarization caused by K+ flowing through voltage-gated channels out of the cell

d. representing the portion of the action potential, where Na+ entry depolarizes the neuron, opening up additional voltage-dependent Na+ channels that allow in even more Na+

The point marked 3, on the figure, can be described as __________. a. a period of increased K+ permeability lasting longer than needed to restore the resting state b. a period of time when all gated Na+ and K+ channels are closed c. Na+ channels are inactivating and K+ channels are open d. representing the portion of the action potential, where Na+ entry depolarizes the neuron, opening up additional voltage-dependent Na+ channels that allow in even more Na+ e. a voltage change brought on by the accumulation of graded potentials arriving at the axon hillock

d. the point in time when Na+ entry declines and the slow voltage-gated K+ channels open

The point marked 4, on the figure, can be described as __________. a. a period of increased K+ permeability lasting longer than needed to restore the resting state b. a voltage change brought on by the accumulation of graded potentials arriving at the axon hillock c. representing the portion of the action potential, where Na+ entry depolarizes the neuron, opening up additional voltage-dependent Na+ channels that allow in even more Na+ d. the point in time when Na+ entry declines and the slow voltage-gated K+ channels open e. representing a point where only the leakage channels are open

c. the period of increased K+ permeability that typically lasts longer than needed to restore the resting state Hyperpolarization: Some K+∙ channels remain open, and Na+∙ channels reset. The period of increased K+ permeability typically lasts longer than needed to restore the resting state. As a result of the excessive K+ efflux before the potassium channels close, a hyperpolarization is seen on the AP curve as a slight dip following the spike. Also at this point, the Na+ channels begin to reset to their original position by changing shape to reopen their inactivation gates and close their activation gates.

The point marked 5, on the figure, can be described as ________. a. when all gated Na+ and K+ channels are closed b. a voltage change brought on by the accumulation of graded potentials arriving at the axon hillock c. the period of increased K+ permeability that typically lasts longer than needed to restore the resting state d. when Na+ channels are inactivating and K+ channels are opening e. representing the portion of the action potential, where Na+ entry depolarizes the neuron, opening up additional voltage-dependent Na+ channels that allow in even more Na+

d. the distribution, across the cell membrane, of large anionic cytoplasmic proteins, Na+, K+, and Cl- The distribution, across the cell membrane, of large anionic cytoplasmic proteins, Na+, K+, and Cl- determines the resting membrane potential. At rest the membrane is impermeable to the large anionic cytoplasmic proteins, very slightly permeable to sodium, approximately 25 times more permeable to potassium than to sodium, and quite permeable to chloride ions. These resting permeabilities reflect the properties of the leakage ion channels in the membrane. Potassium ions diffuse out of the cell along their concentration gradient much more easily than sodium ions can enter the cell along theirs. K+ flowing out of the cell causes the cell to become more negative inside. Na+ trickling into the cell makes the cell just slightly more positive than it would be if only K+ flowed. Therefore, at resting membrane potential, the negative interior of the cell is due to a much greater ability for K+ to diffuse out of the cell than for Na+ to diffuse into the cell.

The resting membrane potential of neurons is determined by __________. a. the same mechanisms as found in the electrical system in your house, the flow of electrons b. the leakage of Na+ out of cells and K+ into cells as driven by an electrical gradient set up by the Na+/K+ ATPase c. the flow of K+ and Na+ against their concentration gradients through voltage-dependent ion channels d. the distribution, across the cell membrane, of large anionic cytoplasmic proteins, Na+, K+, and Cl-

b. The absolute refractory period The absolute refractory period is associated with the opening of the Na+ channels until they begin to reset to their original resting state. When a patch of neuron membrane is generating an AP and its voltage gated sodium channels are open, the neuron cannot respond to another stimulus, no matter how strong. This period, from the opening of the Na+ channels until the Na+ channels begin to reset to their original resting state, is called the absolute refractory period (see figure below). It ensures that each AP is a separate, all-or-none event and enforces one-way transmission of the AP.

Which of the following begins with the opening of the Na+ channels and ends when the Na+ channels begin to reset to their original resting state? a. The depolarization phase of an action potential b. The absolute refractory period c. The relative refractory period d. The hyperpolarization phase of an action potential e. The repolarization phase of an action potential

d. An action potential occurs completely when threshold is met and does not happen at all if threshold is not met.

Which of the following best describes the all-or-none phenomenon? a. Unless all of the stimuli are summated both spatially and temporally at the initial segment of an axon, an action potential can not be triggered. b. At the axon terminals, either all of the neurotransmitter molecule are released in vesicles, or no neurotransmitter will enter the synapse. c. If the number of Na+ entering the cell depolarizes to a subthreshold voltage, a weaker action potential is triggered. d. An action potential occurs completely when threshold is met and does not happen at all if threshold is not met.

c. Threshold stimulus The threshold stimulus will result in an action potential in a neuron. A threshold stimulus depolarizes the membrane to -55mV and triggers an action potential. A subthreshold stimulus depolarizes the membrane but fails to reach the voltage required to open voltage-gated channels and trigger an impulse. In a neuron, stimuli are summated (added together) spatially and temporally in order to reach threshold.

Which of the following best describes the event that triggers an action potential in a neuron? a. Spatial summation b. Temporal summation c. Threshold stimulus d. Subthreshold stimulus

d. Na+ entering the cell through chemically gated channels

Which of the following could cause a graded depolarization? a. K+ leaving the cell through leakage (nongated) channels b. K+ leaving the cell through voltage-gated channels c. Na+ entering the cell through voltage-gated channels d. Na+ entering the cell through chemically gated channels

d. Hyperpolarization

Which of the following describes a change of membrane potential from -70mV to -75mV? a. A return to normal resting potential b. Reaching threshold c. Depolarization d. Hyperpolarization

d. The repolarization phase of an action potential

Which of the following events begins with opening of potassium gates and the rushing out of K+? a. The depolarization phase of an action potential b. The hyperpolarization phase of an action potential c. The absolute refractory period d. The repolarization phase of an action potential e. The resting state of a neuron

c. Voltage-gated channels Voltage-gated channels open and close in response to changes in the membrane potential. Membrane channels are large proteins, often with several subunits. Some channels, leakage or nongated channels, are always open. Other channels are gated: Part of the protein forms a molecular "gate" that changes shape to open and close the channel in response to specific signals.

Which of the following membrane ion channels open and close in response to changes in the membrane potential? a. Mechanically gated channels b. Leakage (nongated) channels c. Voltage-gated channels d. Chemically gated channels

b. The neuron cannot respond to another stimulus, no matter how strong, because this time point is within the absolute refractory period.

Which of the following results if the neuron is stimulated at the time point indicated by the arrow? a. Only an exceptionally strong stimulus can trigger another action potential because this time point is within the absolute refractory period. b. The neuron cannot respond to another stimulus, no matter how strong, because this time point is within the absolute refractory period. c. Only an exceptionally strong stimulus can trigger another action potential because this time point is within the relative refractory period. d. The neuron cannot respond to another stimulus, no matter how strong, because this time point is within the relative refractory period.

b. Depolarizing graded potential that could have resulted from an increase in extracellular K+ The event shown in the figure is a depolarizing graded potential, a positive deviation from the resting membrane potential. Scenarios that could cause the inside of the cell to become less negative include an influx of Na+ into the cell or from an increase in extracellular K+ which would reduce the degree of K+ leaving the cell through leakage channels. A hyperpolarizing graded potential is a negative deviation (value would have become more negative, not less negative as shown in the example) from the resting membrane potential. This could be caused by an influx of Cl- into the cell or by a decrease in intracellular Na+.

Which option correctly describes the event shown in the figure? a. Hyperpolarizing graded potential that could have resulted from a decrease in intracellular Na+ b. Depolarizing graded potential that could have resulted from an increase in extracellular K+ c. Hyperpolarizing graded potential that could have resulted from an influx of Na+ into the cell d. Depolarizing graded potential that could have resulted from an influx of Cl- into the cell

c. Leakage channels help maintain the resting membrane potential.

Which statement best describes the role of leakage (nongated) channels? a. Leakage channels are only found in the axon of nerve cells where they facilitate action potentials. b. Leakage channels maintain neuronal excitability by preventing a stable resting membrane potential. c. Leakage channels help maintain the resting membrane potential. d. Leakage channels are only found in dendrites where they induce graded potentials.

d. Chemically gated (ligand-gated) channels

Which type of ion channel opens when a neurotransmitter binds to it? a. Leakage (nongated) channels b. Mechanically gated channels c. Voltage-gated channels d. Chemically gated (ligand-gated) channels